The art of wireless communications and its use in emergency, M2M, and security networks has been well developed. In a sub-segment of the technology, also known as mesh networks, subscribers units are used by other units in the network as repeaters thus building a network providing communications from each of the remote subscribers transceivers to a central or collection transceiver. In most instances, the communication paths from each subscriber to such a central unit are fixed and determined during the commissioning of the whole network. Such systems are described, for instance by Burns (U.S. Pat. No. 5,129,096). Such fixed systems have a number of disadvantages, namely, they do not possess autonomous routing reconfiguration capabilities, when for one reason or another, subscribers drop out of the network, either temporarily or permanently, and require the intervention of an operator, to reestablish network integrity through the establishment of new communication links using the remaining resources (subscribers) in the network.
In U.S. Pat. No. 5,455,569 (hereby incorporated by reference and termed the '569 patent), the present inventor described a link layered wireless communication network that overcomes the shortcomings encountered in fixed communication paths wireless networks. particularly, said link layered network, automatically, and without the intervention of an operator, reconfigures the optimal communication paths when external parameters change over time. Typically such a reconfiguration will result in a routing having the minimal possible number of hops between a remote node and the central node.
However, it has been found that under some special circumstances, improvements to the teachings of '569 are required. For instance, the networks described in '569 were originally used mostly for security systems, such systems involve only minimal communications, since only alarm states and infrequent routing updates messages are required. More modern link layered networks have now found applications in a great variety of circumstances, and with new challenges, not contemplated in '569, nor in the present inventor's U.S. Pat. No. 5,974,236 (hereinafter'236). For instance, link layered networks associated with data based systems such as systems of vending machines, require updating not only of alarm systems, but a constant stream of data related to inventory levels and machines status; thus optimization of system throughput becomes important. Furthermore, the addition of new subscribers to existing networks have increased the number of nodes (each node is associated with such a new subscriber and thus includes its own transceiver) in a network, thus increasing the radio message traffic within a network. Furthermore, such network expansion would often involve more modern nodes having greater capacities and capabilities, necessitating new approaches to network throughput optimization. It is possible that a system of “mixed” nodes will degrade over time as the variation in the nodes increase. In addition, this potential degradation of the network will be the primary reason for the system to fail because the optimizing algorithms in place for years or decades could not anticipate variations unknown at the time the algorithms were written.
Link layered networks are now also used in sub-metering systems, whereby, means are provided to meter energy utilization (and demand rate) for a given location (i.e. an office building with multiple tenants), as well as the usage and demand rate for each tenant, and said means are interfaced each to a communication node that reports that information first to the node associated with the central meter (to ascertain correct summation of demand and utilization), and from there to a “command center.” That command center can be either the utility company itself, or even an energy management system associated with the building and engaged in load optimization. Such communications between the central metering system at each such location and a command center may involve the use of other subscribers, which are not necessarily a part of the meter reading network. There is therefore a need to provide for optimized network throughputs in networks containing nodes of differing capacities and capabilities.
Other applications of link layered network also involve both mobile (such as taxicabs) and stationary “points of sales” where credit cards readers are networked into a link layered network reporting to a central node. As is the case with submetering systems, there is a need to provide for optimized communications to a central node, often using subscribers having nodes of diverse capacities.
The prior link layered network art ('569 and '236), while teaching adequately how individual nodes can be dropped from, or incorporated in a network, fails to provide for special cases, for instance when a whole network is shut down. As the numbers of, as well as the density of nodes in a link layered network are increased, particular problems are encountered, for instance, recovery of a network from an extreme state. An extreme state could result from local power failure, rolling black outs, or even the intentional shut down of a network for various reasons. In the prior art, when such a system is “awakened” after such a failure, many of the nodes, simultaneously, seek to reestablish their best routing by sending out messages that elicit responses from neighboring nodes, thus allowing the re-incorporation of a node into the network. In such larger networks, one runs into the problem of excessive traffic and thus congestion, and failure to timely reestablish communication links, particularly after power outages or intentional shut down of the network, when all subscribers, almost simultaneously seek to reestablish communication routes to the central transceiver node. There is therefore a need for an optimized method of restarting a network without encountering such radio traffic congestion.
Furthermore, new subscriber additions also bring about networks that have transceivers of different capabilities, capacities and characteristics, necessitating both optimization of throughput as well as routing in such networks. Typically, newer technology will have greater capacity per nodes (where capacity is understood to be the size of each packet transmitted). Flammer in U.S. Pat. No. 6,480,497, attempts to optimize net throughput in mesh networks by modifying signal characteristics in response to determining performance metrics of the last received signal, over a given link between two nodes. This approach has three major shortcomings. Firstly, optimization is carried out only on each link, and the teachings do not assure that such optimization will necessarily result in overall network optimization, since the optimization of throughput process on each link itself may simply add a large number of additional unnecessary hops. A second shortcoming is that in link layered networks of the present invention, it is necessary to adapt the system to such signal characteristics variations between nodes, rather than modifying them as Flammer '497 suggests. A third shortcoming of a system of the type described in '497 is that it lacks “directionality” and does not possess “sequentiality” of the optimization process of each link between any two nodes. Thus, often, an optimizing process of the link between any two nodes may require re-optimization of neighboring links causing incessant system oscillations and excessive radio traffic in the network. There is therefore a need to optimize routing of packets in link layered network, despite having incongruity in nodes packets capabilities and capacities, such as baud rate and packet length, and therefore consolidate in one single network nodes of vastly different characteristics. There is further a need for such an optimization process which will not by itself throw the network into constant oscillations and readjustments. Furthermore, such optimization should promulgate within the whole network, standards generated from the then designated central node.
Flammer et al in U.S. Pat. No. 5,488,608 (the '608 patent) suggests that traffic in a network can be routed, without having a network directory at each node, and indeed, when intermixing older technology with newer technology in link layered network, there are practical limitations on local memory, preventing sometimes, storing all possible routings between any two points at each node (as taught in the present inventor's U.S. Pat. No. 5,974,236). However, the '608 approach relies on assigning to each node an identifier indicative of the nodes coordinate locations, and using those coordinates for facilitating routing of packets to and from such nodes. This approach, however will not work, when part of the nodes have variable geography, such as mobile nodes contemplated in '236 and the present invention, nor will that approach work when the link layered network is, for instance a submetering network, where all the nodes are typically, essentially, at the same location or in the same building.
The lack of information on the link layer level in the header of the '608 packets will often result in packets being transmitted almost randomly, till they find the destination node to which they were intended, or worse, result in circular transmissions (where the same packet is handled between a sub group of all nodes that does not include the destination node, in essence repeatedly) causing unnecessary radio traffic congestion in the network. There is therefore a need to provide for a link layered network in which circular transmissions and radio traffic overload is avoided, that does not rely on the specific knowledge of the coordinates of each of the nodes in the network, and optimizes and accommodates future, currently unknown nodes yet to be implemented on the network.
When a practical link layered network is installed, some of its nodes, by virtue of their geographical location, height and type of antenna, level of RF noise and interference, or even universality of capacity, or a combination of these factors, become preferential repeaters. Such nodes can be termed “Critical Nodes” in that they serve as a hub for a large number of routes from remote transmitters to the then designated central node (from here on we will term this the “central node”, but it should be understood that according to the teachings of '236, any node in the system can be designated the “then central node” without interfering with the operation of the system).
Such critical nodes in the prior art would thus become overloaded and transmit from remote nodes to the central node a disproportionate amount of the network's messages, creating a localized over utilization of the available broadcasting spectrum, and in some cases, these result in loss of packets. There is therefore a need to equalize the traffic load to other less critical nodes, even though, some messages will no longer be transmitted with the minimum number of hops, as taught in '569 and '236, but be optimally transmitted, so as to optimize both the utilization of the various nodes and the radio channel. This by spreading the transmissions over a wide geographic area in the system as well as allowing the number of hops required to transmit a packet from a remote node to the central node to be greater than minimal.